Conventionally, there has been a planar inverted F antenna which includes a first radiation element and a second radiation element which is placed parallel to a ground plane and is extended along a longitudinal direction of the first radiation element. The second radiation element is shorter that the first radiation element. The second radiation element is disposed in a manner that the second radiation element substantially widens a width of the first radiation element at around a feeding point (see Patent Reference 1, for example).
Although the conventional planar inverted F antenna has a low profile and a wider bandwidth is achieved, an optimization for downsizing is not conducted.